CLIMATE

TEMPERATURE

Temperature varies across the earth.

Temperature variations are related to the amount of the sunlight received and the nature of the surface area receiving the sunlight.

• Land and Water Differential

INSOLATION AND LATITUDE

Sunlight is called insolation.

At any given time only limited areas of the Earth receive the sun’s vertical (direct) rays.

Because of the curvature of the earth the higher latitudes receive insolation at oblique angles.

The higher the latitude the more oblique the suns rays.

INSOLATION AND LATITUDE

The differing amounts of insolation divide the earth into several climatic zones including:

• The North and South Tropical Zones

• The North and South Mid-latitude Zones

• The North (Arctic) and South (Antarctic) Polar Zones

VARIATIONS IN PRESSURE

Cold temperatures create conditions of dense, sinking air and high pressure.

High temperatures create conditions of expanding, rising air and low pressure.

Temperature variations and the rotation of the Earth create a pattern of belts of pressure variations.

WIND

Winds are the means by which the atmosphere attempts to balance the uneven distribution of pressure (temperature) over the Earth’s surface.

• Coriolis Effect

OCEAN CURRENTS

Surface winds are the primary control of the major ocean surface currents.

The major surface currents move in broad circular patterns called gyres. The gyres flow clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

OCEAN CURRENTS AND CLIMATE

In general the nature of the winds and ocean currents bring warm waters along the east coasts of continents and cooler waters along the west coasts of continents.

• California Coast

• New Jersey Coast

PRECIPITATION

Precipitation varies across the earth’s surface.

For precipitation to occur you need to have moist air rise.

There are three mechanisms to get air to rise including:

• Convection

• Cyclonic (Frontal)

• Orographic

DISTRIBUTION OF PRECIPITATION - LATITUDE

Precipitation varies with latitude.

In general, the higher the latitude the lower the precipitation.

The main factors affecting precipitation include:

• Temperature

• Pressure

THE KOPPEN CLASSIFICATION SYSTEM

The most widely used climate classification is based on temperature and precipitation patterns and is referred to as the Köppen System.

Dr. Köppen recognized that major vegetation associations reflect the local climate.

HUMID TROPICAL (A) CLIMATES

The humid tropical regions all have the coolest month of the year above 64.4°F (18°C).

The tropical rain forest (Af) has steady precipitation throughout the year (no month below 2.4 inches).

The tropical monsoon (Am) climate has a distinct rainy season.

The tropical savanna (Aw) climate has a wet summer and a dry winter.

ARID CLIMATES

The first concentration of deserts occur in the vicinity of 25 to 35 degrees North and South of the equator which are directly related to the subtropical high pressure cells, of subsiding, dry (few clouds), stable air and divergent winds.

• Sahara

• Australia

ARID CLIMATES

The second concentration of deserts is located at higher latitudes and within continental interiors remote from moisture carrying winds.

Rain shadow effects have a lot to do with the Great Basin in the U.S., Western China and the Patagonia desert in Argentina.

In most cases, the deserts are core areas of dry conditions surrounded by slightly moister steppe climates.

The dryer the area is, the more variability there is in precipitation.

MID-LATITUDE CLIMATES

The Mid-Latitude climates are divided into the mesothermal and microthermal climatic groups.

It is the degree of change that distinguishes one from another.

MESOTHERMAL CLIMATES

There are three distinct mesothermal climates.

• Mediterranean Climate

• Humid Subtropical Climate

• Marine West Coast

MEDITERRANEAN CLIMATE

The Mediterranean climate appears with remarkable regularity in the vicinity of 30° to 40° of latitude along the west coasts of each landmass.

The alternative controls of subtropical high pressure in summer and westerly wind movement in winter cause this climate of warm, dry summers, mild, moist winters.

HUMID SUBTROPICAL CLIMATES

The humid subtropical climate extends inland from continental east coasts between 20° to 40° North and South of the equator.

Located at similar latitudes as Mediterranean Climates on the eastern side of continents.

Summers can be as hot and humid as the tropical areas.

MARINE WEST COAST CLIMATE

Proximity to the sea and prevailing onshore winds make the Marine West Coast climate one of the most temperate in the world.

Found between 40° and 65° and influenced by the westerlies, this climate receives ample precipitation throughout the year.

Unlike the Humid Subtropical Climate, the Marine West Coast Climate has mild to cool summers.

HUMID MICROTHERMAL (D) CLIMATES

The Humid Microthermal Climate Regions are found at high latitudes and are thus only found in the Northern Hemisphere between 35° and 75°N.

• No ocean modification.

They have cold winters and variable lengths of summer depending on latitude.

POLAR CLIMATES

There are two types of Polar climates:

Tundra (ET)

Warmest month between 32° to 50°F

Polar Ice Cap (EF)

No month above 32° F

HIGHLAND CLIMATES

Complexity is the hallmark of highland climate. Every mountain range of significance is composed of a mosaic of climate that would be difficult to see on a small scale map.